In electrical machines such as traction motors in electrically powered vehicles, the roller bearings are exposed to the passage of current. When the amount of current passing through a roller bearing exceeds a certain density at the contact points between the rolling elements and the raceways, the surfaces of the raceways and thus the bearing itself are destroyed. Roller bearings which are exposed to the passage of current must therefore be protected from such current at least to the extent that the current density does not reach or exceed the danger limit in the roller bearing. It is known that current bridges can be provided outside the roller bearing for this purpose. In these applications, the contact resistance must be calculated so that the roller bearing is protected from the current.
It is also known that the cage or the seal of the roller bearing can be provided as a current bridge. EP 787,915 A1 describes a roller bearing with rolling elements which consist of electrically non-conductive material. One of the bearing rings has a seal or the like attached to it. This seal touches both bearing rings and is designed to be electrically conductive, so that the electrical current is carried away from the roller bearing or so that electrical signals can be conducted through the roller bearing.
The rolling elements in this known solution are either made completely of non-conductive ceramic material or are covered with a coating of this material. The seal consists of a suitable plastic. This arrangement has certain disadvantages and drawbacks. For example, the problem in the prior art with the arrangement shown in Patent EP 787 915A1 is that the seal is a sliding seal which tends to wear at its lip portion. The erosion of the sliding element necessitates replacement from time to time. Furthermore, it has been observed that there is a build up at the seal lip which effects the current carrying capacity.